In spacecraft that are in the take-off or landing phase through the earth's atmosphere, or spacecraft exposed to extreme thermal stress in orbit around the earth, it is necessary that the generated heat is safely and reliably removed. Evaporation heat exchangers are employed for this purpose.
The basic principle of operation of such heat exchangers lies in that, the medium to be cooled, referred to herein as coolant, circulates in an active liquid circulating circuit for the heat removal, by bringing the coolant into heat transferring contact with a medium to be evaporated, which is stored in a supply container. The evaporated medium in the form of vapor is then discharged out of the spacecraft into the surroundings.
In order to optimally use the medium to be evaporated referred to herein as "evaporant", the evaporation must be as complete as possible, whereby it is important to ensure as good a thermal contact as possible for the heat transfer between the cooling liquid and the evaporant to transform the latter into vapor to be discharged.
In a conventional heat exchanger described, for example, in German Patent Publication DE-PS 3,718,873, (Muschelknautz et al., published on Nov. 10, 1988), the cooling liquid, or rather coolant, flows through individual channels extending through a processing or heat exchange space, into which the medium to be evaporated is sprayed in droplet form through an inlet valve. In a second conventional evaporation heat exchanger, the cooling liquid or coolant flows openly through the processing space, while the medium to be evaporated is caused to flow through individual channels usually arranged in bundles passing through the heat exchange space. The cooling liquid is, in addition, forced into a meandering flow path through screens arranged in the processing space or chamber.
The danger of icing or ice formation exists in such an evaporation heat exchanger, if it is operated with water as the cooling liquid. In order to prevent this danger, it may be necessary, under certain circumstances, to influence the evaporation temperature of the evaporant, which is often ammonia.